Titanium tetrachloride has been produced by a chlorinating reaction of titanium-containing raw material, and high titanium-containing raw material for production of titanium tetrachloride contains a few percent of impure oxides. Most of the impure oxides are chlorinated as similarly as titanium oxide, and since most of the impure chlorides have a high melting point, they are separated and recovered as a solid component, and treated as waste material.
Therefore, it is considered desirable to reduce chlorine loss during the chlorinating of titanium-containing raw material as the amount of impurities in titanium-containing raw material is smaller.
However, the amount of deposit of high grade titanium-containing raw material is limited, and there is a tendency that the price of the high titanium-containing raw material is increasing reflecting great demand recently in South-East Asia.
The high titanium-containing raw material is conventionally available in the market in the form of synthetic rutile in which a low-grade ilmenite ore as a starting material is improved in quality by a wet method such as the Benelite method.
On the other hand, a quality improving method is also known in which impurities in titanium-containing raw material are selectively chlorinated by chlorine gas so that the impurities are removed in the form of chlorides.
In the above selective chlorinating method, chlorine gas is reacted with titanium-containing raw material first, so that iron in the titanium-containing raw material is separated and removed in the form of chloride.
At this time, among oxides contained in the titanium-containing raw material, Ti3O5 or the like, which is one of titanium suboxides, has a tendency to be chlorinated at the same time of chlorinating of iron since it is easy to be chlorinated compared to titanium oxide (TiO2). This is not desirable since it may cause loss of titanium and chlorine gas. This is a problem when the selective chlorinating method is used in quality improving in titanium-containing raw material.
The selective chlorinating method is known as a technique in which only the iron component in titanium-containing raw material is selectively chlorinated, separated and removed so that grade of titanium oxide in titanium-containing raw material is improved, as mentioned above. In particular, for example, Japanese Unexamined Patent Application Publication No. Showa 62 (1987)-167223 discloses a method in which ilmenite ore is preliminarily reduced before selective chlorinating of the ilmenite ore.
The publication discloses that, according to this method, the ratio of divalent iron in the ilmenite ore is increased, and as a result, the ratio of separating and removing of iron by the selective chlorinating can be increased.
However, in the above method, there may be a case in which a part of titanium oxide in ilmenite ore is reduced and titanium suboxide is generated. Titanium suboxide is easier to be chlorinated compared to titanium oxide, and, during selective chlorinating, there may be a case in which chlorinating of titanium suboxide is promoted in addition to chlorinating of iron oxide. When titanium suboxide is chlorinated, there is a new problem that the amount of titanium oxide in titanium ore is reduced.
Furthermore, since the selective chlorinating reaction of titanium ore is an endothermic reaction, the temperature around reaction part may be decreased and a certain reaction rate cannot be maintained unless heat is supplied from the outside. Since a further cost may be required to maintain the reaction temperature, there is room for improving in this problem.
As mentioned above, a technique is required in which selective chlorinating of ilmenite ore or titanium slag can be efficiently promoted.